EP0025820B1

EP0025820B1 - Heat sensitive recording sheet

Info

Publication number: EP0025820B1
Application number: EP19800103392
Authority: EP
Inventors: Akihiro Yamaguchi; Keizaburo Yamaguchi; Hisamichi Murakami
Original assignee: Mitsui Toatsu Chemicals Inc
Current assignee: Mitsui Toatsu Chemicals Inc
Priority date: 1979-06-18
Filing date: 1980-06-18
Publication date: 1986-02-05
Also published as: EP0025820A1; CA1149613A; EP0030563B1; EP0030563A1; JPS6025277B2; JPS56191A; WO1980002820A1; US4407892A; EP0030563A4; DE3071443D1

Description

Background of the Invention

(1) Field of the Invention

This invention relates to an improved heat sensitive recording sheet containing a novel developer.

(2) Description of the Prior Art

A so-called dye color development type heat sensitive recording sheet is well known in the art, according to which a coupler consisting of electron donative, color assuming compounds such as triphenylmethane series, fluoran series, phenothiazine series, auramine series, spiropyran series, and the like (hereinafter simply referred to as coupler), and a developer consisting of a solid acid selected from clays such as activated clay, phenol compounds (FR-A-2,367,618), aromatic carboxylic acids, aromatic polyvalent metal salts, 2,2'-bisphenol sulfides (US-A-3,560,229, and the like, are brought into contact with each other by heating to obtain a developed color image by the application of the color reaction therebetween.
Generally, the heat sensitive recording sheet is required as conditions for performance thereof which . the sheet should possess to be colorless or light colored itself, to have a fast developed color image as well as an excellent performance for color development immediately after the preparation of the sheet or after a long term storage of the sheet without lowering thereof, to be sufficiently stable to light or moisture, and further to be prepared economically. The developer for heat sensitive recording, which has already been proposed, and sheets coated with the developer have both merits and demerits from the standpoint of performance, and these sheets have such drawbacks that color develops prior to heating on reproduction to produce blushing because two reactants are brought into contact with each other to be coated on a substrate, that they have poor storage stability of a developed image such as light resistance and water resistance, and that color does not develop instantly on heating, which demands further an improved heat sensitive recording sheet.
The color development property by heating of 4,4'-isopropylidenediphenyl (bisphenol A) exclusively used at present is of clear, but fastness properties to light of the developed color image are not satisfactory.

Summary of the Invention

An object of this invention is to provide an improved heat sensitive recording sheet.
Another object of this invention is to provide a heat sensitive recording sheet which gives a developed color image having an excellent fastness to light and water resistance.
A further object of this invention is to provide a heat sensitive recording sheet according to which a decrease in density of developed image by light with time is very little.
The present invention provides the following heat sensitive recording sheet.
A heat sensitive recording sheet prepared by coating a coupler, developer and binder on a sheet substrate, or by impregnating such therein, characterized in that said developer is one or more than one of the compounds represented by formula (I):
where each R is an alkyl radical of from 1 to 12 carbon atoms, a cycloalkyl radical of from 3 to 10 carbon atoms, an aralkyl radical of from 7 to 10 carbon atoms, or a phenyl radical, and is identical to or different from each other, M is a polyvalent metal, and n is zero, 1 or 2.
The present invention further provides a heat sensitive recording sheet which contains one or more than one of the compounds represented by the general formula (I) as developer, and may further contain a heat fusible material which has a melting point of from 50° to 190°C and is substantially colorless at room temperature said heat fusible material being acetanilide, urea, diphenylamine, biphenyl, naphthalene, methyl p-hydroxybenzoate, stearic acid, zinc stearate, ethyleneglycol ester stearate ortriphenylphosphate. The heat sensitive recording sheet containing these heat fusible materials generally increases more and more the rate of color development on heating, and lowers the temperature of color development.

Detailed Description of the Preferred Embodiments

Examples of the compounds represented by the general formula (I) include, but not to be limited thereto,

zinc 2,2'-bis(p-cresol)sulfide,
zinc 2,2'-bis(p-tert-butylphenol)sulfide,
nickel 2,2-bis(p-tert-butylphenol)sulfide,
zinc 2,2'-bis(p-tert-butylphenol)sulfone,
nickel 2,2'-bis(p-tert-butylphenol)sulfone,
zinc 2,2'-bis(p-tert-amylphenol)sulfone,
zinc 2,2'-bis(p-cyclohexylphenol)sulfide,
zinc 2,2'-bislp-cyclohexylphenol)sulfoxide,
zinc 2,2'-bis(p-cyclohexylphenol)sulfone,
nickel 2,2'-bis(p-cyclohexylphenol)sulfone,
cobalt 2,2'-bis(p-cyclohexylphenol)sulfone,
zinc 2,2'-bis(p-cumylphenol)sulfide,
nickel 2,2'-bis(p-cumylphenol)sulfoxide,
zinc 2,2'-bis(p-cumylphenol)sulfone,
magnesium 2,2'-bis(p-cumylphenol)sulfone,
nickel 2,2'-bis(p-cumylphenol)sulfone,
manganese 2,2'-bis(p-cumylphenol)sulfone,
zinc 2,2'-bis(p-phenylphen61)sulfide,
calcium 2,2'-bis(p-phenylphenol)sulfone,
nickel 2,2'-bis(p-phenylphenol)sulfone,
cobalt 2,2'-bis(p-phenylphenol)sulfone,
zinc 2,2'-bis(p-tert-octylphenol)sulfide,
nickel 2,2'-bis(p-tert-octylphenol)sulfide,
cobalt 2,2'-bis(p-tert-octylphenol)sulfide,
zinc 2,2'-bis(p-octylphenol)sulfoxide,
zinc 2,2'-bis(p-tert-octylphenol)sulfone,
nickel 2,2'-bis(p-tert-octylphenol)sulfone,
magnesium 2,2'-bis(p-tert-octylphenol)sulfone,
cobalt 2,2'-bis(p-tert-octylphenol)sulfone,
calcium 2,2'-bis(p-tert-octylphenol)sulfone,
barium 2,2'-bis(p-tert-octylphenol)sulfone,
zinc 2,2'-bis(p-dodecylphenol)sulfide,
nickel 2,2'-bis(p-dodecylphenol)sulfide,
cobalt 2,2'-bis(p-dodecylphenol)sulfide,
zinc 2,2'-bis(p-dodecylphenol)sulfoxide,
calcium 2,2'-bis(p-dodecylphenol)sulfoxide,
nickel 2,2'-bis(p-dodecylphenol)sulfone,
magnesium 2,2'-bis(p-dodecylphenol)sulfone,
zinc 2,2'-bis(p-nonylphenol)sulfide,
magnesium 2,2'-bis(p-nonylphenol)sulfide,
calcium 2,2'-bis(p-nonylphenol)sulfoxide,
zinc 2,2'-bis(p-nonylphenol)sulfone,
chromium 2,2'-bis(p-nonylphenol)sulfone,
nickel 2,2'-bis(p-nonylphenol)sulfone,
cadmium 2,2'-bis(p-nonylphenol)sulfone,
magnesium 2,2'-bis(p-nonylphenol)sulfone, and the like.

The developer represented by the general formula (I) as mentioned above can be prepared by such a process as described below. For example, the developer is prepared by reacting to be formed an alkali metal salt of one member selected from bisphenol compounds consisting of p-substituted 2,2'- bisphenolsulfide, 2,2'-bisphenolsulfoxide, and 2,2'-bisphenolsulfone compounds and a water soluble polyvalent metal salt in a solvent in which both salts are soluble. That is, the developer is prepared by a process in which one gram equivalent of the bisphenol compound is reacted with 2 gram equivalents or more of hydroxides, alkoxides, or the like of alkali metal to form an alkali metal salt of bisphenol compounds, or an aqueous solution, alcohol solution or water-alcohol mixed solution thereof, and then one gram equivalent or more of the water soluble polyvalent metal salt is reacted therewith to form the developer.
Examples of the water soluble polyvalent metal salt used for the preparation of the developer employed in the present invention include chlorides, salts with inorganic acids such as sulfuric acid and nitric acid, salts with organic acids such as oxalic acid and acetic acid, and the like of polyvalent metals such as magnesium, calcium, aluminium, zinc, tin, nickel, barium, strontium, cadmium, manganese, cobalt, chromium, and the like.
The heat fusible material used in the present invention is a solid which is colorless at room temperature, or is almost colorless to such an extent that no feeling of color development is substantially given when impregnated in the heat sensitive recording sheet, and is such a material as to have a sharp melting point at a temperature suitable for recording on reproduction recording, that is, at a temperature in the neighbourhood of from 50° to 190°C, and to dissolve either one or both of a coupler and a developer represented by the general formula (I) at a fused state thereof.
A typical process for the preparation of the heat sensitive recording sheet of the present invention will be described below. The coupler usable in the present invention include various materials which develop color by a fusion reaction thereof with a developer represented by the general formula (I). Examples of the coupler include electron donating and color assuming compounds such as

3,3'-bis(4-dimethylaminophenol)-6-dimethylaminophthalide(crystal violet lactone),
3-diethylamino-6-methyl-7-chlorofluoran,
3-diethylamino-7-chlorofluoran,
3-cyclohexylamino-6-chlorofluoran,
3-diethylamino-7-dibenzylaminofluoran,
3-diethylamino-6-methyl-7-phenylaminofluoran,
1,3,3-trimethylindolino-6'-chloro-8'-methoxyspiropyran,
3-methyl-2,2'-spiro bis(benzo [f] chromene), and the like.

A colorless or light colored coupler described as above, a developer represented by the general formula (I), or a mixture of a coupler, developer, and a heat fusible material is thoroughly mixed with a solution prepared by dissolving a binder in water or an organic solvent, or with a dispersion of the binder therein to prepare a mixed solution.
Examples of the binder used for the preparation of the mixed solution include synthetic polymers such as styrene butadiene polymer, polyvinylalcohol, carboxymethylcellulose, hydroxyethylcellulose, polystyrene, vinylchloride-vinylacetate copolymer, and acacia, and natural or modified natural polymers. Examples of the solvent used include organic solvents such as benzene, toluene, acetone, methylene chloride, ethyl acetate, and cyclohexane, and water.
The mixed solution thus obtained is coated to be dried on a substrate such as paper, natural or synthetic resin film, and the like. The mixed solution may be allowed to flow into the substrate to be impregnated therein. The method of mixing and method of coating described as above are not limited to the heat sensitive recording sheet of the present invention. For example, the coupler and/orthe heat fusible material are mixed with a binder solution, and separately the developer and/or the heat fusible material are mixed with a binder solution. Then both mixtures thus obtained may be mixed together for coating on the substrate, or these two mixtures may be separately coated on the substrate to be coated thereon twice. Both mixtures may be coated on the same surface or surfaces separate from each other of the substrate, or may be coated on different substrates respectively.
The coating weight is generally above 0.5 g/m², preferably in the range of from 1 to 10 g/m² on dry weight basis.
A relative amount of each component of the heat sensitive recording sheet is wide variable, but suitably in the range of from 1 to 15 parts by weight of the coupler, 1 to 95 parts by weight of the developer represented by the general formula (I), 1 to 40 parts by weight of the binder, and zero or 0.5 to 200 parts by weight of the heat fusible material respectively on dry weight basis.
According to the heat sensitive recording sheet of the present invention, the coupler and developer are brought into contact with each other, while they are prepared, coated, and dried before being heated. Nevertheless, the heat sensitive recording sheet of the present invention have such advantages that no blushing occurs due to color development, that stability thereof with time is kept at a high level without lowering in color development performance by exposure thereof to light before reproduction, that the color development is effected instantly on heating, and that the developed image has excellent light resistance and water resistance.
The present invention will be further explained by the following Examples.
The method of measurement and assessment for various performances of the recording sheet are shown below.

1) Developed color density:

A recording sheet is subjected to heat color development under the following conditions,
by use of Thermotest.Rhodiaceta (manufactured by SETARAM Co.; Type 7401
Reflectance (I) is measured in 10 minutes after color development by heating by use of an amber filter for TSS type Hunter color difference meter (manufactured by Toyo Seiki Co., Ltd.). The lower the reflectance is, the higher the developed color density becomes.

2) Fade resistance to light of developed image:

A sheet developed according to the procedure in 1) is lighted for a time period of from 30 minutes to 6 hours by use of a carbon arc lamp, and the following reflectances are measured by use of Hunter color difference meter in the same manner as in 1),

lo: reflectance of sheet before color development,
Is: reflectance of color developed sheet before lightening,
In: reflectance of color developed sheet n hours after lightening.

The fade resistance to light of developed image is represented by use of the above reflectances as
A higher degree of residue is preferable.

3) Storage stability:

A sheet before color development and a color developed sheet are stored 6 months at 25°C, and the reflectance of the sheet before color development and that of the color developed sheet before storage are represented by Ko and Ko' respectively, and those after storage are represented by K and K' respectively. The smaller the values of differences of K-Ko and K'-Ko' are, the more the storage stability are preferable.

4) Water resistance

A color developed recording sheet is kept in water for 2 hours, and a change in color density of a color developed image is observed with the naked eye.

Example 1

Dispersions are prepared separately from solution A and B respectively by use of a sand grinding mill, and two separate dispersions are mixed at such a ratio as 3 parts of solution A to 67 parts of solution B. The mixture is coated on fine paper and dried so that the coating weight may be in the range of from 2.5 to 3.5 g/ m² on dry basis to obtain a heat sensitive recording sheet.

Example 2

Both solutions as above are subjected to the same procedure as in Example 1 to prepare dispersions, and the dispersions thus obtained are mixed at such a ratio as 3 parts of solution A to 134 parts of solution B. The mixture is coated on a fine paper and dried so that the coating weight may be in the range of from 2.5 to 3.5 g/m² on dry basis to obtain a heat sensitive recording sheet.

Comparative Example

The procedure of Example 1 is repeated except that bisphenol A is used instead of nickel 2,2'-bis(p-tert-octylphenol)sulfone in Example 1 to obtain a heat sensitive recording sheet.

Examples 3 to 8

The procedure of Example 1 is repeated by use of nickel 2,2'-bis(p-tert-butylphenol)sulfide (Example 3), zinc 2,2'-bis(p-tert-butylphenol)sulfoxide (Example 4), magnesium 2,2'-bis(p-tert-octylphenol)sulfone (Example 5), and cobalt 2,2'-bis(p-tert-octylphenol)sulfone (Example 6) respectively instead of nickel 2,2'- bis(p-tert-octylphenol)sulfone in Example 1 to obtain a heat sensitive recording sheet.
Further the procedure of Example 2 is repeated by use of calcium 2,2'-bis(p-tert-butylphenol)sulfone (Example 7), and nickel 2,2'-bis(p-cumylphenol)sulfone (Example 8), instead of nickel 2,2'-bis(p-tert-octylphenol)sulfone in Example 2 to obtain a heat sensitive recording sheet.
Results of performance assessment for heat sensitive recording sheets obtained in Examples 1 to 3 and Comparative Example are shown in Table 1, and results of performance assessment for heat sensitive recording sheets obtained in Examples 3 to 8 are shown in Table 2.
Results of Examples 1 to 8 show that every color developed image has excellent water resistance.

Claims

1. A heat sensitive recording sheet prepared by coating a coupler, developer and binder on a sheet substrate, or by impregnating such therein, characterized in that said developer is one or more than one of the compounds represented by formula (I):

where each R is an alkyl radical of from 1 to 12 carbon atoms, a cycloalkyl radical of from 3 to 10 carbon atoms, an aralkyl radical of from 7 to 10 carbon atoms, or a phenyl radical, and is identical to or different from each other, M is a polyvalent metal, and n is zero, 1 or 2.

2. A heat sensitive recording sheet claimed in claim 1, wherein M in the general formula (I) is magnesium, calcium, aluminium, zinc, tin, nickel, cobalt, barium, strontium, cadmium, manganese, or chromium.

3. A heat sensitive recording sheet claimed in claim 2, wherein M in the general formula (I) is nickel, zinc, cobalt, magnesium, or calcium.

4. A heat sensitive recording sheet claimed in claim 1, wherein R in the general formula (I) is tert-butyl, amyl, tert-octyl, nonyl, dodecyl, or cumyl radical.

5. A heat sensitive recording sheet prepared by coating a coupler, developer and binder on a sheet substrate, or by impregnating such therein, characterized in that said developer is one or more than one of the compounds represented by formula (I)

where each R is an alkyl radical of 1 to 12 carbon atoms, a cycloalkyl radical of 3 to 10 carbon atoms, an aralkyl radical of 7 to 10 carbon atoms, or a phenyl radical, and is identical to or different from each other, M is a polyvalent metal, and n is zero, 1 or 2, and said sheet further contains a heat fusible material which has a melting point of from 50° to 190°C and is substantially colorless at room temperature, said heat fusible material being acetanilide, urea, diphenylamine, biphenyl, naphthalene, methyl p-hydroxybenzoate, stearic acid, zinc stearate, ethyleneglycol ester stearate or triphenylphosphate.